Silver-alloy based sputtering target

ABSTRACT

The present invention relates to a sputtering target comprising a silver alloy that contains 5-25% by weight of palladium, based on the total amount of silver alloy, and has a mean grain size in the range of 25-90 μm.

The present invention relates to a sputtering target that comprises a silver alloy, and also to a production process for said sputtering target.

On account of its good reflection properties, silver is a customary coating material in the field of optical data storage, display applications and in optoelectronics. Depending on the usage environment and further adjoining layers, silver has a tendency to corrosion, which can lead to impairment of the reflection properties and to failure of the component.

It is known that the corrosion properties can be improved when alloying elements are added to the silver. Thus EP 2 487 274 A1, for example, describes a silver alloy that contains up to 1.5% by weight of indium and has a mean grain size in the range of 150-400 μm. U.S. Pat. No. 7,767,041 describes bismuth-containing silver alloys.

JP 2000-109943 describes silver alloys that contain 0.5-4.9 atom % palladium.

EP 1 736 558 describes a silver alloy for use as reflection coating. This silver alloy contains at least two alloying elements, wherein the first alloying element is aluminum, indium or tin, and the second alloying element can be selected from a multiplicity of further metallic elements.

The higher the amount of added alloying element, the higher the corrosion stability on the one hand, but, on the other hand, the risk that the reflection properties can be adversely affected also increases.

In principle, such reflection coatings can be applied to a substrate via differing coating processes. A preferred process is sputtering, wherein sputtering targets are used. As is known to those skilled in the art, a sputtering target is taken to mean the material that is to be sputtered in a cathode atomization system.

In the chemical composition of the sputtering target, the desired properties of the coating that is to be produced must be taken into account. If, for example, a silver-based reflection coating of high corrosion stability is to be produced via the sputtering process, the sputtering target can consist of a silver alloy containing corrosion-inhibiting alloying elements.

An important criterion that a sputtering target should conventionally meet is a very uniform sputtering rate, in order to permit in this manner the formation of a coating having a layer thickness fluctuation as low as possible. High fluctuations in layer thickness inter alia also adversely affects the reflection behavior of a silver coating. Furthermore, a uniform sputtering behavior promotes high target utilization and therefore increases the process efficiency.

In addition, a suitable sputtering target should permit deposition at the lowest possible arc rate. “Arcing” denotes local spark discharges on the sputtering target. Owing to the spark discharge, the sputtering target material becomes fused locally and small splashes of said fused material can pass onto the substrate that is to be coated and generate defects there.

Therefore, the sputtering target material must be provided in such a manner that, firstly, it possesses the desired end properties of the coating that is to be applied (e.g. good reflection properties with the highest possible corrosion stability), and, secondly, it has a uniform sputtering rate and the lowest possible arcing, in order to minimize the layer thickness fluctuation and the number of defects in the coating. An improvement in one aspect (e.g. optimizing the layer properties with respect to the planned use) should not proceed at the cost of the second aspect (sputtering properties that are as good as possible). However, in practice, it is frequently found that it is difficult to satisfy both aspects simultaneously.

An object of the present invention is to provide a sputtering target with which a silver-based reflection coating of high corrosion resistance and low layer thickness fluctuation can be produced at low arc rate. A further object of the present invention is to provide a suitable process for the production of such a sputtering target.

This object is achieved by a sputtering target comprising a silver alloy

-   -   that contains 5-25% by weight of palladium, based on the total         amount of silver alloy, and     -   has a mean grain size in the range of 25-90 μm.

Owing to the relatively high fraction of palladium in the silver alloy, a reflection coating having high corrosion stability may be produced using the sputtering target according to the invention. In the context of the present invention, it was surprisingly found that, despite the high fraction of palladium in the silver alloy of the sputtering target, a very uniform sputtering rate and therefore a very low layer thickness fluctuation may be achieved in the deposited coating, if the silver alloy has a mean grain size in the range of 25-90 μm.

Preferably, the silver alloy contains the palladium in an amount of 7-23% by weight, more preferably 9-21% by weight. In a preferred embodiment, the silver alloy contains the palladium in an amount of 7-13% by weight. Alternatively, it can also be preferred that the silver alloy contains the palladium in an amount of 17-23% by weight. These quantitative details of palladium each are based on the total amount of the silver alloy.

Optionally, the silver alloy can contain yet further alloying elements as unavoidable impurities. These unavoidable impurities can be metallic impurities. Preferably, these unavoidable impurities are kept as low as possible and are present in total preferably in an amount of less than 0.5% by weight, more preferably less than 0.05% by weight. This can be ensured, for example, if the starting metals that are used for producing the silver alloy already have a sufficiently high purity. In a preferred embodiment, the silver alloy contains 5-25% by weight of palladium, whereas further metallic elements are present (e.g. as unavoidable impurities) in total in an amount of less than 0.5% by weight, more preferably less than 0.05% by weight, or even less than 0.01% by weight in the silver alloy. The quantitative details are based on the total weight of the silver alloy.

In a preferred embodiment, the mean grain size of the silver alloy is in the range of 30-85 μm, still more preferably in the range of 35-70 μm.

The sputtering properties of the silver alloy can be further optimized when the grains of the silver alloy have a defined axial ratio. In a preferred embodiment, the grains of the silver alloy have a mean axial ratio of at least 60%, more preferably at least 70%, or at least 75%, or even at least 85%. Preferably, the axial ratio of the grains is a maximum of 100%.

As is explained hereinafter in still more detail in the description of the measurement methods, for determining the mean grain axial ratio, the height (maximum dimension of a grain in the thickness direction (i.e. perpendicular to the sputtering surface) of the sputtering target) and width (maximum dimension of a grain perpendicular to the thickness direction, or in parallel to the sputtering surface) of grains are determined. For the grains in each case the value of the quotient of grain height to grain width and finally the mean value of said quotient values is calculated (in each case multiplied by 100 to be reported in %). The axial ratio of the individual grains (i.e. the quotient of height and width of the respective grains) is determined on a section perpendicularly to the sputtering surface. The sputtering surface is the surface from which atoms are detached by bombardment with high-energy particles.

The sputtering properties of the silver alloy can, in addition, be further optimized when the grains of the silver alloy have a low variation (in %) of the grain size. Preferably, the silver alloy of the sputtering target has a grain size variation of less than 15%, more preferably less than 11%, still more preferably less than 9%, or even less than 7%.

Since the silver alloy of the sputtering target is a crystalline material, X-ray diffraction reflections are correspondingly found in the X-ray diffraction. The intensity of the respective X-ray diffraction reflection describes preferred orientations in the crystal lattice and textures of the alloy. In a preferred embodiment, the variation of the intensity ratio of the second-most intensive X-ray diffraction reflection to the intensity of the most intensive X-ray diffraction reflection is less than 35%, more preferably less than 25%. It has been found that silver alloys that comply with this condition have a grain orientation that is highly advantageous for a uniform sputtering rate.

Preferably, the silver alloy of the sputtering target has an oxygen content of less than 100 ppm by weight, more preferably less than 50 ppm by weight, still more preferably less than 30 ppm by weight.

Preferably, the sputtering target consists of the abovedescribed silver alloy.

Depending on the application, the geometry of the sputtering target can vary. The sputtering target can, for example, be planar (e.g. in the form of a disk or a plate) or tubular.

Depending on the planned application, the dimensions of the sputtering target can also vary over a broad range. For example, the planar sputtering target can have an area in the range from 0.5 m² to 8 m². The tubular sputtering target can have, for example, a length in the range from 0.5 to 4 m.

If necessary, the sputtering target can further be applied to a substrate, e.g. to a backplate. The bonding of the sputtering target to the substrate can proceed, for example, by means of solder (e.g. indium). Positive-locking application to a backplate is also possible. This is known in principle to those skilled in the art.

In a further aspect, the present invention relates to a process for producing the above-described sputtering target in which a melt containing silver and palladium is allowed to solidify in order to obtain a shaped body, the shaped body is heated to a forming temperature of at least 200° C. and then subjected to at least one forming step, and the shaped body is in addition subjected to at least one recrystallization.

The silver- and palladium-containing melt can be produced by familiar methods known to those skilled in the art, for example a melting furnace (e.g. in an induction melting furnace, in particular a vacuum-induction melting furnace). For this purpose silver metal and palladium metal can be placed into the melting furnace in suitable amounts (i.e. in order to obtain a silver alloy having a Pd fraction of 5-25% by weight) and fused. As starting material, also, a silver alloy that already contains palladium as alloying element can also be used. In order to keep the amount of unwanted impurities as low as possible, it can be advantageous to use the starting metals in sufficiently high purity already. For example, the silver and the palladium can each be used in a purity of at least 99.5%. The melting operation is usually carried out under vacuum and/or an inert gas atmosphere (e.g. argon).

Subsequently, the melt can be poured into a mold or gravity die (e.g. a graphite mold). If the melt is allowed to cool and solidify in this mold, a solid shaped body is obtained.

As mentioned above, the shaped body is heated to a forming temperature of at least 200° C. and then subjected to at least one forming step. In addition, the shaped body is subjected to at least one recrystallization. As described in more detail hereinafter, the recrystallization can proceed during the forming. However, it is also possible that the recrystallization is carried out after the forming. In addition, it is possible that a recrystallization is carried out not only during the forming but also after the forming.

The forming can proceed, for example, by rolling, forging, swaging, stretching, extrusion or pressing, or a combination of two or more of said forming processes. These forming processes are known to those skilled in the art.

In principle, it is possible in the context of the process according to the invention that the forming proceeds only in a single forming step (e.g. rolling step). Alternatively, it can be preferred that at least two, more preferably at least four, forming steps (preferably rolling steps) are carried out, e.g. 2-10 or else 4-8 forming steps (preferably rolling steps).

If two or more rolling steps are carried out, the direction of rolling can in each subsequent rolling step conform to the direction of rolling of the preceding rolling step, or be rotated by about 180°. Alternatively, it is also possible that, in the case of two or more rolling steps, cross-rolling can proceed, i.e. in each successive rolling step, the direction of rolling is rotated in each case by about 90° in comparison with the preceding rolling step (either in each case clockwise or in each case counter-clockwise). It is also possible that the direction of rolling is rotated in each rolling step by about 360°/n in comparison with the preceding rolling step (either in each case clockwise or in each case counterclockwise), wherein n is the number of rolling steps.

In the context of the present invention, it has proved to be advantageous if each forming step is preferably carried out at a forming rate ε of at least 2.5 s⁻¹, more preferably at least 5.5 s⁻¹, still more preferably at least 7.0 s⁻¹. The upper limit of the forming rate is not critical. However, for processing reasons, it can be advantageous if the forming rate does not exceed a value of 20 s⁻¹ or else 15 s⁻¹.

The mean forming rate (i.e. in the case of a plurality of forming steps, the mean of the forming rates) can be, for example, at least 3.2 s⁻¹, more preferably at least 5.5 s⁻¹, still more preferably at least 7.0 s⁻¹, or even at least 8.5 s⁻¹. The upper limit of the mean forming rate is not critical. However, for processing reasons it can be advantageous if the mean forming rate does not exceed a value of 20 s⁻¹ or else 15 s⁻¹.

As is known to those skilled in the art, the forming rate is calculated according to the following equation:

$ɛ = {\frac{2\pi \; n}{60\sqrt{r^{\prime}}} \cdot \sqrt{\frac{R}{H_{0}}} \cdot {\ln \left( \frac{1}{1 - r^{\prime}} \right)}}$

-   -   wherein     -   n is the speed of rotation of the roll,     -   H₀ is the thickness of the shaped body before the rolling step,     -   r′=r/100 where r=reduction of the thickness of the shaped body         per rolling step and     -   R is the roll radius.

On the basis of their specialist knowledge, those skilled in the art can therefore readily carry out a rolling step in such a manner that a preset forming rate is achieved, by presetting the reduction in thickness per rolling step.

In the process according to the invention, the shaped body is subjected to at least one recrystallization. This can be a dynamic or static recrystallization. As is known to those skilled in the art, a dynamic recrystallization proceeds during forming. During the static recrystallization no forming proceeds. Determination of the recrystallization temperature of a given alloy under defined processing conditions is readily possible to those skilled in the art on the basis of their general specialist knowledge.

Preferably, the shaped body is subjected to at least one dynamic recrystallization (i.e. during forming, that is to say while the shaped body is subjected to one or more forming steps) and to at least one static recrystallization.

Preferably, the forming temperature to which the shaped body is heated before the forming is at least 500° C., more preferably at least 600° C., or even at least 700° C. In the context of the present invention, the shaped body can also be further actively heated (e.g. by an external heat source) during the forming. When the shaped body, however, is not significantly cooled during forming, a further active heating via an external heat source is not required during the forming steps.

In principle, the process according to the invention can also comprise one or more cold forming steps. Alternatively, it is possible that the process according to the invention does not comprise cold forming.

Preferably, the static recrystallization takes place after the forming by annealing the formed shaped body. Preferably, the annealing temperature is at least 500° C., more preferably at least 600° C., or even at least 700° C. The time duration of annealing can vary over a broad range. For example, an annealing time from 0.5 to 5 hours can be stated.

The forming, and where it is carried out the static recrystallization after the forming, can proceed under vacuum, in an inert gas atmosphere (e.g. nitrogen) or else in air.

After the static recrystallization (e.g. by the abovedescribed annealing), the shaped body can be allowed to cool. Alternatively, it can be preferred that the shaped body, after the static recrystallization, is quenched, for example by immersion into a water bath.

In a further aspect, the present invention relates to the use of the abovedescribed sputtering target for the production a reflection layer.

The reflection layer can be, for example, the reflection layer in a display or a monitor screen. On account of the high quality and very low layer thickness fluctuation, the reflection layer can also be used in flexible displays or monitor screens.

The invention will be described in more detail with reference to the following examples.

EXAMPLES I. Measurement Methods

The parameters to which reference is made in the present application are determined using the following measurement methods:

Mean Grain Size

The mean grain size M was determined using the linear intercept method (DIN EN ISO 643) according to the following equation:

M=(L×p)/(N×m)

-   -   wherein     -   L: length of the measurement line     -   p: number of measurement lines     -   N: number of intercepted bodies     -   m: enlargement

The values were determined at 3×3=9 different measurement sites at each of 3 depths: 0 mm, 3 mm and 6 mm

Variation of Grain Size

From the grain sizes M, the variation can be determined in accordance with the two following equations (as value A1 or alternatively as value B1):

A1=((M _(max) −M _(ave))/M _(ave))×100

B1=((M _(ave) −M _(min))/M _(ave))×100

-   -   where     -   M_(max): maximum value of the grain sizes     -   M_(min): minimum value of the grain sizes     -   M_(ave): mean grain size

In the context of the present application, the higher of the two values (A1 or B1) is used to establish the grain size variation.

Mean Axial Ratio (in %) of the Grains

For determination of the mean grain axial ratio, the height (maximum dimension of a grain in the thickness direction (i.e. perpendicular to the sputtering surface) of the sputtering target) and width (maximum dimension of a grain perpendicular to the thickness direction or parallel to the sputtering surface) of grains are determined. For the grains in each case the value of the quotient of grain height to grain width and finally the mean value of said quotient values is calculated (in each case multiplied by 100 for the figure in %).

In the determination of height and width of grains, the following procedure is used: from the sputtering target, a section is prepared perpendicular to the sputtering surface. On this section at least two regions each having at least 40 grains are selected. For each of these grains, the height thereof (i.e. maximum dimension or extent in the thickness direction of the sputtering target) and also width thereof (i.e.

maximum dimension perpendicular to the thickness direction) are determined. This proceeds, for example, using a light microscope with a size scale or with a scanning electron microscope. The value of the quotient of height and width is formed for each of the grains. From these quotient values the mean value is calculated.

Variation of the Intensity Ratio between the Secondmost Intensive X-Ray Diffraction Reflection and the Most Intensive X-ray Diffraction Reflection

X-ray diffraction measurements are performed on the sputtering target at 5 different sites. CuK_(α1) radiation, two-circle diffractometer with Bragg-Brentano geometry, measurement area approximately 10 mm².

For each X-ray diffraction measurement, the intensity I₂ (according to peak height) of the secondmost intensive diffraction reflection and the intensity I₁ (peak height) of the most intensive diffraction reflection are determined, and the intensity ratio R=I₂/I₁ is formed from these values.

The variation of the intensity ratio can be determined in accordance with the two following equations (as value A2 or alternatively as value B2):

A2=((R _(max) −R _(ave))/R _(ave))×100

B2=((R _(ave) −R _(min))/R_(ave))×100

-   -   where     -   R_(max): maximum value of the intensity ratios     -   R_(min): minimum value of the intensity ratios     -   R_(ave): mean value of the intensity ratio values R

In the context of the present application, the higher of the two values (A2 or B2) is used to establish the variation of the X-ray diffraction intensity ratio.

Oxygen Content

The oxygen content was determined according to the measurement method COHNS using a setup from Leco.

II. Production of Sputtering Targets

Example 1 Production of a Sputtering Target Consisting of a Silver Alloy with 20% by Weight of Palladium

Silver and palladium, each of a purity of 99.9%, were placed into a vacuum induction melting furnace in amounts corresponding to the predetermined end composition and were melted at 1200° C. and 10⁻¹ mbar (initial weight: 3.5 kg). The melt was poured into a graphite mold and the melt was allowed to solidify.

The resultant shaped body was preheated to 750° C. (1 hour). The forming proceeded in 4 rolling steps.

The thickness of the shaped body before the rolling and after each rolling step and also the respective thickness reduction and forming rate are stated in table 1 for each rolling step. The total degree of forming was 60%.

TABLE 1 Thickness, thickness reduction and forming rate in example 1 Thickness Thickness Rolling Thickness reduction reduction Forming step [mm] [mm] [%] rate [1/s] 0 (i.e. 20 0 0 before rolling) 1 16 4 20.0 8.1 2 13 3 18.8 8.7 3 10 3 23.1 11.0 4 8 2 20.0 11.4

As already mentioned above, the forming rate is calculated in a known manner according to the following equation:

$ɛ = {\frac{2\pi \; n}{60\sqrt{r^{\prime}}} \cdot \sqrt{\frac{R}{H_{0}}} \cdot {\ln \left( \frac{1}{1 - r^{\prime}} \right)}}$

-   -   wherein     -   n is the speed of rotation of the roll,     -   H₀ is the thickness of the shaped body before the rolling step,     -   r′=r/100 where r=reduction of the thickness of the shaped body         per rolling step and     -   R is the roller radius.

In example 1, at a roller speed of 40 rpm and a roller radius of 300 mm, this gave forming rates for the respective rolling steps of 8.1 to 11.4 s⁻¹.

The degrees of forming of the respective rolling steps were in the range of 18-23%.

After the fourth rolling step, a plate of approximately 500×100×8 mm was obtained. This plate was annealed at 750° C. for 1 hour for the recrystallization and then quenched in a water bath.

The silver alloy had the following properties:

Mean grain size: 53 μm Mean axial ratio of the grains:   90% Variation of the grain size:  5.6% Variation of the intensity ratio between 21.7% the secondmost intensive diffraction reflection and the most intensive diffraction reflection: Oxygen content: 12 ppm by weight

FIG. 1 shows a cut section image (section perpendicular to the sputtering surface) of the silver alloy. The picture was prepared using a light microscope, after etching the surface with HNO₃ at 70° C.

Finally the plate was machined (milled) and bonded with indium.

Example 2 Production of a Sputtering Target Consisting of a Silver Alloy having 5% by Weight of Palladium

Silver and palladium were placed into a vacuum induction melting furnace in amounts corresponding to the predetermined end composition and melted at 1200° C. and 10⁻¹ mbar. The melt was poured into a graphite mold and the melt was allowed to solidify.

The resultant shaped body was preheated to 250° C. (1 hour). The forming proceeded in 8 rolling steps.

The thickness of the shaped body before the rolling and after each rolling step and also the respective thickness reduction and forming rate for each rolling step are shown in table 2.

TABLE 2 Thickness, thickness reduction and forming rate in example 2 Thickness Thickness Rolling Thickness reduction reduction Forming step [mm] [mm] [%] rate [1/s] 0 (i.e. 20 0 0 before rolling) 1 18 2 10.0 2.7 2 16 2 11.1 3.0 3 14.5 1.5 9.4 2.9 4 13 1.5 10.3 3.2 5 11.5 1.5 11.5 3.6 6 10 1.5 13.0 4.1 7 9 1 10.0 3.8 8 8 1 11.1 4.3

In example 2, the forming rates for the respective rolling steps were in the range from 2.7 to 4.3 s⁻¹.

The degrees of forming of the respective rolling steps were in the range of 9-13%.

After the eighth rolling step, a plate of approximately 500×100×8 mm was obtained. This plate was annealed for the recrystallization at 750° C. for 1 hour and then quenched in a water bath.

The silver alloy had the following properties:

Mean grain size: 49 μm Mean axial ratio of the grains:  83% Variation of the grain size: 8.2%

Finally the plate was machined and bonded with indium.

Example 3 Production of a Sputtering Target Consisting of a Silver Alloy Containing 10% by Weight of Palladium

Silver and palladium were placed into a vacuum induction melting furnace in amounts corresponding to the predetermined end composition and melted at 1200° C. and 10⁻¹ mbar (initial weight: 1.8 kg). The melt was poured into a graphite die having a round cavity (i.e. disk shape) and the melt was allowed to solidify.

The resultant shaped body was preheated to 900° C. (1 hour). The forming proceeded in 4 rolling steps. A cross-rolling was carried out, i.e. after each rolling step the shaped body was rotated by 90° clockwise.

The thickness of the shaped body before rolling and after each rolling step and also the respective thickness reduction and forming rate for each rolling step are stated in table 3.

TABLE 3 Thickness, thickness reduction and forming rate in example 3 Thickness Thickness Rolling Thickness reduction reduction Forming step [mm] [mm] [%] rate [1/s] 0 (i.e. 20 0 0 before rolling) 1 16 4 20.0 8.1 2 13 3 18.8 8.7 3 10 3 23.1 11.0 4 8 2 20.0 11.4

After the fourth rolling step, a disk of approximately 160×8 mm was obtained.

No final annealing for recrystallization was carried out.

The silver alloy had the following properties:

Mean grain size: 59 μm Axial ratio of the grains: 62% Variation of the grain size: 14%

Finally the plate was machined and bonded with indium.

Example 4 Production of a Sputtering Target Consisting of a Silver Alloy with 15% by Weight of Palladium

Silver and palladium were placed into a vacuum induction melting furnace in amounts corresponding to the predetermined end composition and melted at 1200° C. and 10⁻¹ mbar (initial weight: 1.8 kg). The melt was poured into a graphite die having a round cavity (i.e. disk shape) and the melt was allowed to solidify.

The resultant shaped body was preheated to 750° C. (1 hour). The forming proceeded in 4 rolling steps. A cross-rolling was carried out, i.e. after each rolling step, the shaped body was rotated by 90° clockwise.

The thickness of the shaped body before rolling and after each rolling step and also the respective thickness reduction and forming rate for each rolling step are stated in table 4.

TABLE 4 Thickness, thickness reduction and forming rate in example 4 Thickness Thickness Rolling Thickness reduction reduction Forming step [mm] [mm] [%] rate [1/s] 0 (i.e. 20 0 0 before rolling) 1 16 4 20.0 8.1 2 13 3 18.8 8.7 3 10 3 23.1 11.0 4 8 2 20.0 11.4

After the fourth rolling step, a disk of approximately 160×8 mm was obtained. This plate was annealed for the recrystallization at 800° C. for 1.5 hours and then quenched in a water bath.

The silver alloy had the following properties:

Mean grain size: 60 μm Axial ratio of the grains: 80% Variation of the grain size: 10%

Finally the plate was machined and bonded with indium.

Comparative Example 1 Production of a Sputtering Target Consisting of a Silver Alloy Containing 20% by Weight of Palladium

Silver and palladium were placed into a vacuum induction melting furnace in amounts corresponding to the predetermined end composition and melted at 1200° C. and 10⁻¹ mbar. The melt was poured into a graphite mold and the melt was allowed to solidify.

The resultant shaped body was not preheated. The forming proceeded as cold rolling in 10 rolling steps.

The thickness of the shaped body before the rolling and after each rolling step and also the respective thickness reduction and forming rate for each rolling step are stated in table 5.

TABLE 5 Thickness, thickness reduction and forming rate in comparative example 1 Thickness Thickness Rolling Thickness reduction reduction Forming step [mm] [mm] [%] rate [1/s] 0 (i.e. 20 — — — before rolling) 1 18.5 1.5 7.5 2.3 2 17 1.5 8.1 2.5 3 15.5 1.5 8.8 2.7 4 14 1.5 9.7 3.0 5 13 1 7.1 2.7 6 12 1 7.7 2.9 7 11 1 8.3 3.2 8 10 1 9.1 3.5 9 9 1 10.0 3.8 10  8 1 11.1 4.3

In example 2, the forming rates for the respective rolling steps were in the range from 2.3 to 4.3 s⁻¹.

After the tenth rolling step, a plate of approximately 500×100×8 mm was obtained.

The silver alloy had the following properties:

Mean grain size: 95 μm Axial ratio of the grains: <50% Variation of the grain size: >18%

Finally, the plate was machined and bonded with indium.

Determination of the Layer Thickness Uniformity of Reflection Coatings

Using the sputtering target (palladium content of 20% by weight) produced in example 1, a coating was sputtered onto a glass substrate (at 500 V DC, 0.2 A, 100 W). The layer showed a layer thickness deviation of less than 5%, measured at 10 points of the glass substrate. The arc rate was markedly below 1 μarc/h.

Using the sputtering target produced in comparative example 1 (palladium content of 20% by weight), a coating was likewise sputtered onto a glass substrate (at 500 V DC, 0.2 A, 100 W). The layer showed a layer thickness deviation of more than 10%, measured at 10 points of the glass substrate.

25

As is clear from the examples, using the sputtering target according to the invention reflection coatings can be produced with a very constant layer thickness. The arc rate can also be kept very low. Since the sputtering targets in addition have a relatively high palladium fraction, a very good corrosion resistance is ensured. 

1. A sputtering target comprising a silver alloy that contains 5-25% by weight of palladium, based on the total amount of silver alloy, and has a mean grain size in the range of 25-90 μm.
 2. The sputtering target as claimed in claim 1, wherein the silver alloy has a variation of grain size of less than 15%, and/or the grains of the silver alloy have a mean axial ratio of at least 60%.
 3. The sputtering target as claimed in claim 1, wherein the silver alloy has a variation of the intensity ratio between the secondmost intensive X-ray diffraction reflection and the most intensive X-ray diffraction reflection of less than 35%, and/or the silver alloy has an oxygen content of less than 100 ppm by weight.
 4. The sputtering target as claimed in claim 1, wherein further metallic elements, where present, are present in the silver alloy in total in an amount of less than 0.5% by weight.
 5. A process for producing the sputtering target as claimed in claim 1, wherein a melt containing silver and palladium is allowed to solidify in order to obtain a shaped body, the shaped body is heated to a forming temperature of at least 200° C. and then subjected to at least one forming step, and the shaped body is in addition subjected to at least one recrystallization.
 6. The process as claimed in claim 5, wherein the forming step is a rolling, a forging, a swaging, a stretching, an extrusion or a pressing.
 7. The process as claimed in claim 6, wherein the rolling is a cross-rolling.
 8. The process as claimed in claim 1, wherein each forming step is carried out at a forming rate of at least 2.5 s⁻¹.
 9. The process as claimed claim 1, wherein the shaped body is subjected to at least one dynamic recrystallization and/or at least one static recrystallization.
 10. The process as claimed in claim 9, wherein the dynamic recrystallization takes place during the forming, and/or the static recrystallization proceeds after the last forming step.
 11. The process as claimed in claim 5, wherein the forming temperature to which the shaped body is heated before the first forming step is at least 500° C., and/or the static recrystallization after the last forming step proceeds via an annealing at an annealing temperature of at least 500° C.
 12. The process as claimed in claim 9, wherein the shaped body is quenched after the static recrystallization. 13-14. (canceled) 